Problem: Simplify. Rewrite the expression in the form $a^n$. $\dfrac{a^{-13}}{a^{-6}}=$
Recall that $\dfrac{x^n}{x^m}=x^{n-m}$. $\begin{aligned} \dfrac{a^{-13}}{a^{-6}}&=a^{-13-(-6)} \\\\ &= a^{-13+6} \\\\ &= a^{-7} \end{aligned}$